Water on the moon boiled away in massive quantities in a cataclysmic evaporation event during the moon's birth, bolstering the theory that a Mars-sized body collided with the Earth to form its only natural satellite, scientists say.

Researchers examined rocks collected by astronauts during NASA's Apollo lunar landing missions, as well as a meteorite that originated on the moon to make the find. They looked for traces of zinc, and found the ratios of heavy to light isotopes are greater than on Earth, which suggests the moon went through an intense evaporation event early in its formation.